1. Technical Field
The disclosure generally relates to a method and an apparatus for processing an image, and more particularly, to a method and an apparatus for designing a restoration filter and a method and an apparatus for restoring an image by using the restoration filter.
2. Background
The requirement of consumers to image quality has been increasing along with the widespread of digital cameras and digital camcorders. However, the image quality may be seriously affected by unresolved imaging defects in optical designs, lens errors, nonlinear characteristics and noises of sensors, and incorrect focusing or tuning at the time of image capturing.
Generally speaking, an optical system or imaging system can be represented with a point spread function (PSF), and an image captured by a sensor can be obtained through the convolution of an input image and the PSF of the imaging system. An image formed on the sensor through the optical system is referred to the ideal image if the PSF is an ideal impulse function or its size is approximately equal to a pixel of the sensor. However, in an actual application, the PSF may be enlarged due to diffraction limit, aberration, and incorrect focusing. Accordingly, the bandwidth of the imaging system may be reduced so that the image captured by the imaging system is blurred.
Conventionally, a Wiener filter is usually adopted for processing a captured image, and an inverse filter in the frequency domain is designed by using the PSF of the imaging system, so as to resolve the problem of image blur. However, in this method, the PSF model of the imaging system and the signal-to-noise ratio (SNR) thereof have to be obtained. If either parameter is not precisely obtained, the image restoration performance may be reduced, or noises may even be increased due to improper design.